US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
343 PM EDT Thu Oct 15 2020
 
Valid Sunday October 18 2020 - Thursday October 22 2020
 
Hazards:
- Heavy rain across portions of the Central Plains, the Middle Mississippi Valley, the Great Lakes, 
the Upper Mississippi Valley, and the Northern Plains, Wed-Thu, Oct 21-Oct 22.
- Heavy snow across portions of the Northern Plains and the Northern Rockies, Sun, Oct 18.
- Flooding occurring or imminent across portions of the Lower Mississippi Valley.
- High winds across portions of the Central Rockies, the Central Plains, the Northern Plains, and 
the Northern Rockies, Sun-Mon, Oct 18-Oct 19.
- Much below normal temperatures across portions of the Central Plains, the Upper Mississippi 
Valley, the Northern Plains, and the Northern Rockies, Sun-Thu, Oct 18-Oct 22.
- Much below normal temperatures across portions of the Central Plains, the Upper Mississippi 
Valley, and the Northern Plains, Sun-Tue, Oct 18-Oct 20.
 
Detailed Summary:

The medium range (Sun. Oct 18 - Thurs. Oct 22) is highlighted by anomalous ridging over the East 
Coast and a deep upper trough across the North Central U.S. and the Canadian Prairies. The bulk of 
the hazardous weather potential across the Lower 48 is forecast to be along the periphery of the 
base of the upper trough with wintry weather expected in the northern Rockies. Heavy snow is 
expected Saturday into Sunday there along with considerably cold temperatures spreading east into 
the northern Plains. A strong wind field over Wyoming could lead to strong winds across in portions 
of the state. By Tuesday, the ridge axis pulls back west leading to moderating temperatures in the 
Midwest but much below normal temperatures should persist in the northern High Plains and Rockies.

A shortwave trough in western Canada surges south mid-week and eventually emerges into the northern 
U.S. by Thursday, bringing another round of mountain snow to the northern Rockies. Depending on 
totals, it is possible snow could fall heavily at times Ensemble guidance suggests the potential 
for heavy rainfall in the Midwest but totals and its position are dependent upon the position of 
the trough and also the strength of the ridge along the East Coast. The is ensemble spread in the 
position of the upper trough and the extent of the eastern U.S. ridge which could re-position the 
heavy rainfall area in future forecasts.

Over Alaska, an amplifying upper level trough over the upper Peninsula and most of the mainland is 
likely to be the primary weather driver across the state in the medium range. To start the period, 
the Panhandle can expect wetter than normal conditions but precipitation amounts are forecast to be 
below hazardous thresholds. Drier conditions are likely to return in the Panhandle later in the 
week. Most of the mainland can anticipate a dry and mild stretch of weather into much of next week. 
There is some ensemble support for a storm system in the North Pacific to take aim at the Peninsula 
and Aleutians Wednesday into Thursday, but the ridge position and high spread in 500mb heights 
indicate low confidence in potential impacts to the area at this time.

Mullinax